DE112022001045T5 - semiconductor laser element - Google Patents

Abstract

A semiconductor laser element (1) comprises: a substrate (10); a first semiconductor layer (20) disposed over the substrate (10); a light emitting layer (30) disposed over the first semiconductor layer (20); a second semiconductor layer (40) disposed over the light emitting layer (30); and a groove portion (70) formed at least on the substrate (10) and the first semiconductor layer (20). The second semiconductor layer (40) has a ridge part (40a) for guiding a laser light generated in the light emission layer (30). The width of the ridge part (40a) changes cyclically in accordance with the position in a wave guiding direction of the ridge part (40a). The angle between a side surface (40b) of the ridge part (40a) and the wave guide direction is larger than a critical angle, which is formed by an effective refractive index on an inside of the ridge part (40a) and an outside of the ridge part (40a). The groove part (70) is formed on the outside of the side surface (40b) at least where the width of the ridge part (40a) is small.

Description

TECHNICAL FIELD

The present invention relates to a semiconductor laser element and is suitable for use in processing products, for example.

This application is the result of contract research under the title “Development of advanced laser processing with intelligence based on high-brightness and high-efficiency laser technologies / Development of new light-source/elemental technologies for advanced processing / Development of GaN-based high- power high-beam quality semiconductor lasers for highly-efficient laser processing” of the New Energy and Industrial Technology Development Organization for fiscal year 2016 and is a patent application covered by Article 17 of the Industrial Technology Enhancement Act.

STATE OF THE ART

In recent years, semiconductor laser elements have been used in the processing of various products. In order to improve the processing quality in such a semiconductor laser element, the light emitted by the semiconductor laser element preferably has a high output power and the proportion of a fundamental mode is increased, while a mode of a higher order is cut off as much as possible.

Patent Literature 1 mentioned below describes a semiconductor laser element comprising: an optical waveguide mechanism with a rough surface provided on both side walls of a stripe-shaped ridge portion at the center in the waveguiding direction; and a parallel optical fiber mechanism with a smooth surface provided at both ends in the waveguide direction. The optical fiber mechanism with a rough surface causes a loss in the higher order mode and increases the proportion of the fundamental mode.

REFERENCE LIST

[PATENT LITERATURE]

[PTL 1] Japanese Patent Laid-Open Publication Number H9-246664

SUMMARY OF THE INVENTION

PROBLEM STATEMENT

In the configuration of Patent Literature 1, a ripple (disturbance) may be caused in a vertical far-field pattern. In this case, the shape of the emission light is shifted significantly from an ideal Gaussian shape. This causes a problem that the quality of the laser light emitted from the semiconductor laser element is lowered.

In view of the above problem, an object of the present invention is to provide a semiconductor laser element that can suppress ripple in the vertical far field pattern and increase the fundamental mode content.

TROUBLESHOOTING

A main aspect of the present invention relates to a semiconductor laser element. The semiconductor laser element according to the present invention includes: a substrate; a first semiconductor layer disposed over the substrate; a light emitting layer disposed over the first semiconductor layer; a second semiconductor layer disposed over the light emitting layer; and a groove portion formed at least on the substrate and the first semiconductor layer. The second semiconductor layer has a ridge portion for guiding the laser light generated in the light emitting layer. The width of the ridge part changes in correspondence to the position in a wave guiding direction of the ridge part. The angle between a side surface of the ridge part and the wave guide direction is larger than a critical angle defined by an effective refractive index at an inside of the ridge part and an outside of the ridge part, respectively. The groove part is arranged on the outside of the side surface at least where the width of the ridge part is small.

In the semiconductor laser element of this aspect, because the angle between the side surface of the ridge portion and the waveguide direction is set larger than the critical angle, laser light in the higher order mode is cut off and the proportion of the laser light in the fundamental mode is increased. The groove part is formed at least on the substrate and the first semiconductor layer and is formed on the outside of the side surface at least where the width of the ridge part is small. Accordingly, downward movement of the distribution position of the laser light propagating on the ridge part (waveguide) is less likely to occur, thereby causing a ripple in the vertical far-field pattern is pressed. A ripple in the vertical far field pattern is therefore suppressed and the proportion of the fundamental mode can be increased.

ADVANTAGEOUS EFFECTS OF THE INVENTION

As described above, according to the present invention, a semiconductor laser element that can suppress ripple in the vertical far field pattern and increase the fundamental mode content can be provided.

The effects and significance of the present invention will be illustrated by the following description of an embodiment. However, the embodiment described below is merely an example of the implementation of the present invention. The present invention is in no way limited to the embodiment described herein.

BRIEF DESCRIPTION OF DRAWINGS

• 1 is a plan view schematically showing a configuration of a semiconductor laser element according to an embodiment.
• 2 Fig. 10 is a cross-sectional view schematically showing a configuration of the semiconductor laser element in an AA cross section in the Y-axis positive direction according to the embodiment.
• 3(a) and 3(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 4(a) and 4(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 5(a) and 5(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 6(a) and 6(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 7(a) and 7(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 8(a) and 8(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 9(a) and 9(b) are cross-sectional views for describing a production method of the semiconductor laser element according to the embodiment.
• 10 Fig. 10 is a cross-sectional view schematically showing a configuration of a semiconductor laser device according to the embodiment.
• 11 Fig. 10 is a plan view schematically showing the sizes of a side surface of a burr part according to the embodiment.
• 12(a) Fig. 12 is a graph showing the relationship between a refractive index difference between the inside and the outside of the ridge part and a critical angle according to the embodiment. 12(b) is a graph showing the relationship between a given distance of the side surface in the Y-axis direction and the local minimum value of the width of the side surface in the X-axis direction according to the embodiment.
• 13(a) is a plan view schematically showing a configuration of a semiconductor laser element according to Comparative Example 1. 13(b) and 13(c) are cross-sectional views each schematically showing configurations of a semiconductor laser at an A11-A12 cross-section and an A21-A22 cross-section in the positive Y-axis direction according to Comparative Example 1.
• 14 is a plan view schematically showing a configuration of a semiconductor laser element according to Comparative Example 2.
• 15 contains curve diagrams showing a result of an experiment on a vertical far-field pattern obtained when the structures of the ridge parts of the semiconductor laser elements according to Comparative Examples 1 and 2 are changed.
• 16(a) Fig. 10 is a plan view schematically showing a configuration of a semiconductor laser element according to the embodiment. 16(b) and 16(c) are cross-sectional views each schematically showing configurations of a semiconductor laser at an A31-A32 cross-section and an A41-A42 cross-section in the positive Y-axis direction according to the embodiment.
• 17(a) is a cross-sectional view schematically showing a configuration of a semiconductor laser element according to Modification 1. 17(b) is a cross-sectional view schematically showing a configuration of a semiconductor laser element according to Modification 2.
• 18 is a cross-sectional view schematically showing a configuration of a semiconductor laser element according to Modification 3.
• 19 is a plan view schematically showing a configuration of a semiconductor laser element according to a modification 4.
• 20 is a plan view schematically showing a configuration of a semiconductor laser element according to a modification 5.

It should be noted that the drawings are exemplary of the invention and do not limit the scope of the invention in any way.

PREFERRED EMBODIMENT OF THE INVENTION

An embodiment of the present invention will be described below with reference to the drawings. For convenience, each drawing is labeled with the orthogonal X, Y, and Z axes. The The Z-axis direction is the lamination direction of the layers of the semiconductor laser element, where the positive Z-axis direction is the upward direction.

1 is a plan view schematically showing a configuration of a semiconductor laser element 1.

In the semiconductor laser element 1, a ridge portion 40a extending linearly in the Y-axis direction is provided adjacent to the center in the X-axis direction. The ridge part 40a forms a waveguide WG that guides the laser light. The ridge part 40a conducts the light emission layer 30 (see 2 ) generated and oscillating laser light in the semiconductor laser element 1 along the ridge part 40a. A side surface 40b is provided at each of the ends on the positive side of the X-axis and the negative side of the X-axis of the ridge part 40a. In a plan view, the side surface 40b forms an angle θa or an angle θb with respect to the YZ plane, whereby the width of the ridge portion 40a changes cyclically in accordance with the waveguiding direction (the Y-axis direction) of the ridge portion 40a.

A groove part 70 is provided on each outside of each part where the width in the X-axis direction of the ridge part 40a is small. The groove part 70 has a triangular shape in a plan view, and the width of the groove part 70 in the X-axis direction is different in correspondence to the position in the Y-axis direction. At a position in the Y-axis direction where the width in the X-axis direction of the ridge part 40a becomes small, the width in the X-axis direction of the groove part 70 becomes large. The position in the Z-axis direction of the groove part 70 will be described below with reference to 2 described. The effects provided by the groove portion 70 are discussed below with reference to 16(a) to 16(c) described.

An end surface 1a is the end surface of the ridge part 40a disposed on the positive side of the Y axis, and is the end surface on the emission side of the semiconductor laser element 1. An end surface 1b is the end surface of the burr part 40a disposed on the negative side of the Y -Axis is arranged, and is the end surface on the reflection side of the semiconductor laser element 1. An end surface coating film is formed on each end surfaces 1a, 1b. When light (forward wave) traveling from the end surface 1b side to the end surface 1a side reaches the end surface 1a, a part of the forward wave is emitted as emission light from the end surface 1a in the positive Y-axis direction and becomes a part of the forward wave at the end surface 1a End surface 1a is reflected as light (backward wave) traveling from the end surface 1a side to the end surface 1b side. When the backward wave propagates through the ridge portion 40a in the negative Y-axis direction and reaches the end surface 1b, most of the backward wave is reflected at the end surface 1b as a forward wave. In this way, the light generated in the semiconductor laser element 1 is amplified between the end surface 1a and the end surface 1b to be emitted from the end surface 1a.

2 is a cross-sectional view schematically showing a configuration of the semiconductor laser element 1 of FIG 1 on an AA` cross section seen from the positive Y-axis direction.

As in 2 shown, the semiconductor laser element 1 includes a substrate 10, a first semiconductor layer 20, the light emission layer 30, a second semiconductor layer 40, an electrode member 50, a dielectric layer 60, the groove part 70 and an n-side electrode 80.

The first semiconductor layer 20 is arranged over the substrate 10. The first semiconductor layer 20 is an n-side cover layer.

The light emission layer 30 is arranged over the first semiconductor layer 20. The light emitting layer 30 has a laminated structure in which an n-side light guide layer 31, an active layer 32 and a p-side light guide layer 33 are laminated from below in this order. When a voltage is applied to the semiconductor laser element 1, light is generated and propagates in the light emission layer 30.

The second semiconductor layer 40 is arranged over the light emitting layer 30. The second semiconductor layer 40 has a laminated structure in which an electron barrier layer 41, a p-side cover layer 42 and a p-side contact layer 43 are laminated from below in this order.

In an upper part of the second semiconductor layer 40, the ridge part 40a is formed in the vicinity of the center in the X-axis direction. The ridge part 40a has a shape protruding in the positive Z-axis direction and a ridge shape (projection shape) extending in the Y-axis direction. Because the ridge part 40a is formed, the waveguide WG is shaped to correspond to the area in the X-axis direction of the ridge part 40a. Because the ridge portion 40a is formed, the side surface 40b is formed at the X-axis positive side end and the X-axis negative side end of the ridge portion 40a, respectively. In an upper part of the second semiconductor layer 40, a flat part 40c extending in the X-axis direction from the root of the ridge part 40a is formed.

The electrode member 50 is arranged over the second semiconductor layer 40. The electrode member 50 includes a p-side electrode 51 for applying a voltage and a contact electrode 52 disposed above the p-side electrode 51. The p-side electrode 51 is disposed on the upper surface of the ridge portion 40a. The p-side electrode 51 is an ohmic electrode that is in ohmic contact with the p-side contact layer 43 above the p-side contact layer 43. The contact electrode 52 has a longer shape in the X-axis direction than the ridge part 40a and is in contact with the p-side electrode 51 and the dielectric layer 60.

The dielectric layer 60 is disposed over the p-side cover layer 42 on the outside in the X-axis direction of the ridge portion 40a to confine the light in the ridge portion 40a. Specifically, the dielectric layer 60 is formed continuously from the side surface 40b across the flat part 40c. The dielectric layer 60 is implemented by an insulating film having a smaller refractive index than that of the ridge portion 40a.

The groove part 70 is formed at least on the substrate 10 and the first semiconductor layer 20. In other words, the groove part 70 is formed at least from the lower surface of the substrate 10 to the first semiconductor layer 20 to be in communication with at least the substrate 10 and the first semiconductor layer 20. Specifically, the groove part 70 is formed from the lower surface of the substrate 10 to the first semiconductor layer 20, and a bottom 70a of the groove part 70 is disposed in the first semiconductor layer 20 in the Z-axis direction. The groove part 70 is arranged on the outside of the ridge part 40a in the X-axis direction. The interior of the groove part 70 is filled with air, and the refractive index (refractive index of air) of the groove part 70 is smaller than the refractive index of the first semiconductor layer 20, the light emission layer 30 and the second semiconductor layer 40. The groove part 70 allows the occurrence of a ripple ( Disturbance) in the vertical far field pattern can be suppressed, which will be discussed below with reference to 16(a) to 16(c) is described.

In this embodiment, because the cross section of the groove part 70 has a rectangular shape, the inner end and the outer end in the X-axis direction of the groove part 70 become parallel to the Z-axis direction. Accordingly, in the vicinity of the position P1 at the inner end and in the vicinity of the position P2 at the outer end, a cutting surface is provided in each layer as indicated by a dashed line, and the laser light in a higher order mode is passed through them Cut surface scattered.

The n-side electrode 80 is disposed under the substrate 10 and is an ohmic electrode in ohmic contact with the substrate 10.

The following is with reference to 3(a) until 9(b) a production process for the laser element 1 is described. 3(a) until 9(b) are cross-sectional views similar to that of 2 are similar.

Hereinafter, for the growth of each layer, as organometallic raw materials containing Ga, Al and In, for example, trimethylgallium (TMG), trimethylammonia (TMA) and trimethylindium (TMI), respectively, are used. Ammonia (NH ₃ ) is used as a nitrogen raw material. As a lithography method, a photolithography method using a short wavelength light source, an electron beam lithography method in which rendering is performed directly by an electron beam, a nanoimprint method, or the like can be used. As an etching method, for example, dry etching by reactive ion etching (RIE) using a fluorine-based gas such as CF ₄ or wet etching using hydrofluoric acid (HF) or the like dissolved at 1:10 can be used .

As in 3(a) shown, the first semiconductor layer 20, the light emitting layer 30 and the second semiconductor layer 40 are sequentially by metal organic chemical vapor deposition (MOCVD) on the substrate 10, which is a hexagonal n-type GaN substrate having a main surface in a (0001) plane.

Specifically, on the substrate 10 with a thickness of 400 μm, an n-side cap layer of an n-type AlGaN with 3 μm is grown as the first semiconductor layer 20. Subsequently, the n-side light guide layer 31 of an n-type GaN of 0.2 μm is grown. The active layer 32, which consists of two cycles of a barrier layer made of InGaN and an rlnGaN quantum well layer, is then grown. Subsequently, the p-side light guide layer 33 of a p-type GaN of 0.1 μm is grown. Subsequently, the electron barrier layer 41 made of AlGaN with 10 nm is grown. Subsequently, the p-side cap layer 42 is formed as a 0.66 μm thick stretched superlattice by repeating 220 cycles of a 1.5 nm thick p-type AIGaN layer and a 1.5 nm thick p-type GaN layer bred. Subsequently, the p-side contact layer 43 of a p-type GaN of 0.05 μm is grown.

Then, as in 3(b) shown, the first protective film 91 is formed on the second semiconductor layer 40. Specifically, a 300 nm thick silicon oxide film (SiO ₂ ) is formed as the first protective film 91 on the second semiconductor layer 40 by a plasma CVD (chemical vapor deposition) method using silane (SiH ₄ ). The film forming method for the first protective film 91 is not limited to the plasma CVD method, and, for example, another known film forming method such as a thermal CVD method, a sputtering method, a vacuum evaporation method, or a pulsed laser film forming method may be used. The film forming material of the first protective sheet 91 is not limited to the above, and, for example, a material such as a dielectric or a metal that is selective with respect to etching of the second semiconductor layer 40 may be used.

Then it becomes like in 4(a) 1, the first protective film 91 is selectively removed using a photolithography method and an etching method so that the first protective film 91 having a predetermined shape remains. The predetermined shape is a shape in a plan view of the ridge part 40a of 1 . That is, the predetermined shape is a band-like shape whose width changes in a plan view with respect to the position in the Y-axis direction (the resonator longitudinal direction).

Then be like in 4(b) shown, the p-side contact layer 43 and the p-side cap layer 42 are etched using, as a mask, the first protective film 91 formed with the predetermined shape, thereby forming the ridge part 40a and the flat part 40c in the second semiconductor layer 40.

Specifically, the ridge portion 40a is formed under the first protective film 91 located at the center in the X-axis direction. The ridge part 40a is composed of a projection of the p-side cover layer 42 protruding in the positive Z-axis direction and the p-side contact layer 43 on this projection. The p-side contact layer 43 and the p-side cover layer 42 are etched in the area where the first protective film 91 is not formed, thereby forming the flat part 40c. For etching the p-side contact layer 43 and the p-side cap layer 42, dry etching by an RIE method using a chlorine-based gas such as Cl ₂ may be used.

The height of the ridge portion 40a in the Z-axis direction is not particularly specified, but it is, for example, not smaller than 100 nm and not larger than 1 μm. In order for the semiconductor laser element 1 to operate with a high light output (e.g., Watt class), the height of the ridge portion 40a may be set to not less than 300 nm and not more than 800 nm. In this embodiment, the height of the ridge portion 40a is 650 nm.

The ridge part 40a is formed using, as a mask, the first protective film 91 formed in the predetermined shape. Therefore form as in the top view of 1 1, the side surfaces 40b of the ridge portion 40a have a band-like shape whose width in the X-axis direction changes with respect to the position in the Y-axis direction (the resonator longitudinal direction).

Then, as in 5(a) shown, the first protective film 91 is removed by wet etching using hydrofluoric acid or the like.

Then, as in 5(b) shown, the dielectric layer 60 is formed such that it covers the p-side contact layer 43 and the p-side cover layer 42. Accordingly, the dielectric layer 60 is formed on the ridge part 40a and the flat part 40c. As the dielectric layer 60, for example, a 300 nm thick silicon oxide film (SiO ₂ ) is formed by a plasma CVD method using silane (SiH ₄ ).

Then, a second protective film 92 made of a photoresist is formed on the dielectric layer 60 shown in Fig. (5b). Then, the second protective film 92 is selectively removed, leaving the second protective film 92 only on the flat part 40c. Then, as in 6(a) shown, while the second protective film 92 is used as a mask, only the dielectric layer 60 on the ridge portion 40a is removed by wet etching using hydrofluoric acid to expose the upper surface of the p-side contact layer 43. Then the second protective film 92 is removed. An organic solvent such as acetone can be used to remove the second protective film 92.

Then, as in 6(b) shown, the P-side electrode 51 made of Pd/Pt is formed only on the ridge part 40a by using a vacuum evaporation method and a lift-off method. Specifically, the p-side electrode 51 is formed on the p-side contact layer 43 exposed by the dielectric layer 60. The film forming method for the p-side electrode 51 is not limited to the vacuum evaporation method, and, for example, a sputtering method, a pulsed laser film forming method, or the like may also be used. The electrode material of the p-side electrode 51 only needs to be a material such as a Ni/Au-based material or a Pt-based material that comes into ohmic contact with the second semiconductor layer 40 (the p-side contact layer 43).

Then, as in 7(a) shown, the contact electrode 52 is formed such that it covers the p-side electrode 51 and the dielectric layer 60. Specifically, a negative type resist is patterned by a photolithography method or the like in a part other than the part where the contact electrode 52 is to be formed, and the Ti/Pt/Au contact electrode 52 is formed on the entire area above the substrate 10 a vacuum evaporation method or the like. Then the electrode in an unnecessary part is removed using a lift-off method. Accordingly, the contact electrode 52 can be formed with a predetermined shape on the p-side electrode 51 and the dielectric layer 60. In this way, the electrode member 50 consisting of the p-side electrode 51 and the contact electrode 52 is formed. Then, the lower surface of the substrate 10 is polished with a diamond slurry to thin the substrate 10 to have a thickness of approximately 100 μm.

Then, as in 7(b) shown, a third protective film 93 implemented by a silicon oxide film (SiO ₂ ) is formed on the lower surface (the surface on the negative side of the Z axis) of the polished substrate 10. In 7(b) a state is shown in which the in 7(a) The configuration shown is upside down (a state in which the positive Z-axis direction is the downward direction).

Then, as in 8(a) shown, patterning is performed using a photolithography method and an etching method such that the third protective film 93 remains only at a desired position. That is, the third protective film 93 is selectively removed, leaving the third protective film 93 having a predetermined shape. The predetermined shape corresponds to the shape of the groove part 70 in a plan view of 1 .

Then, as in 8(b) shown, the substrate 10 and the first semiconductor layer 20 are removed by etching using the third protective film 93 as a mask. The etching may be accomplished, for example, by dry etching using Cl ₂ , laser ablation in which an ultraviolet laser light is applied to the material to melt and vaporize the material, or the like. The etching is performed to a depth where the bottom 70a of the groove portion 70 reaches the first semiconductor layer 20. Then, the groove part 70 is formed from the lower surface (the surface on the negative side of the Z axis) of the substrate 10 to the first semiconductor layer 20.

In this embodiment, the condition of etching is set on the substrate 10 and the first semiconductor layer 20, thereby setting the composition ratio (Ga/N) of Ga to N on the surface of the groove part 70 higher than the composition ratio (Ga/N) of Ga to N inside the first semiconductor layer 20. For example, in the case of dry etching using a Cl ₂ gas, if the etching condition is controlled so that physical etching becomes dominant, the elimination of N atoms is promoted and can be a state in in which the number of Ga atoms is relatively large, are generated on the etching surface (the surface of the groove part 70). Normally, in GaN, the composition ratio (Ga/N) has a value close to 1. However, when the etching condition is controlled, the composition ratio (Ga/N) at the etching surface can be made not smaller than 1.5. When oxygen is added to the etching gas, oxidation at the etching surface is promoted and the composition ratio (Ga/N) can be increased.

Then, as in 9(a) shown, the third protective film 93 removed by hydrofluoric acid.

Then, as in 9(b) shown, the n-side electrode 80 on the surface (the main surface the back side of the main surface on which the first semiconductor layer 20 etc. are arranged) is formed on the negative side of the Z-axis of the substrate 10. Specifically, the n-side electrode 80 made of Ti/Pt/Au is formed on the surface on the Z-axis negative side of the substrate 10 by a vacuum evaporation method or the like, and patterning is performed using a photolithography method and an etching method, whereby the n -side electrode 80 is formed with a predetermined shape. In 9(b) For example, the n-side electrode 80 is formed only on the surface on the negative side of the Z-axis of the substrate 10, but the n-side electrode 80 can also be formed in the groove part 70.

Then the semiconductor laser element, which follows the production steps up to 9(b) was subjected to, split along the m-plane (primary splitting), so that the length in the m-axis direction is, for example, 2000 μm. Subsequently, using, for example, an electron cyclotron resonance (ECR) sputtering method, a front cladding film for a cleavage plane from which laser light is emitted is formed to form the end face 1a, and a back cladding film for a cleavage plane is formed on the opposite side to form the end surface 1b. The reflectance of the end surface 1a, 1b is set by adjusting the material, configuration, film thickness, etc. of the cladding film. In order to obtain highly efficient laser characteristics, the reflectance of the end surface 1a on the front side is set to 5% and the reflectance of the end surface 1b on the rear side is set to 95%. Preferably, the reflectance of the end surface 1a is set to about 0.1% to 18%, and the reflectance of the end surface 1b is set to not less than 90%.

Then, the semiconductor laser element that has been subjected to the primary cleavage is cleaved (secondary cleavage) such that the distance in length in the x-axis direction is, for example, 400 μm. This makes the semiconductor laser element 1 of 1 and 2 completed.

10 is a cross-sectional view schematically showing a configuration of a semiconductor laser device 2 with the semiconductor laser element 1 mounted thereon. In 10 A state is shown in which the semiconductor laser element 1 of 2 is upside down (a state in which the Z-axis direction is the downward direction).

The semiconductor laser device 2 includes the semiconductor laser element 1 and a subassembly part 100, and is used for processing a product, for example. The subassembly part 100 includes a base 101, a first electrode 102a, a second electrode 102b, a first adhesion layer 103a and a second adhesion layer 103b.

The base 101 is disposed on the Z-axis positive side of the substrate 10 of the semiconductor laser element 1 and functions as a heat sink. No specific requirements are made here regarding the material of the base 101, and the base 101 may be formed of a material having a thermal conductivity equal to or greater than that of the semiconductor laser element 1, such as a ceramic such as aluminum nitride ( AIN) or silicon carbide (SiC), a diamond (C) formed by CVD, a metal element substance such as Cu or Al, or an alloy such as CuW.

The first electrode 102a is disposed on the Z-axis negative side surface of the base 101, and the second electrode 102b is disposed on the Z-axis positive side surface of the base 101. The first electrode 102a and the second electrode 102b are each a laminate film composed of three metal films such as a 0.1 µm thick Ti film, a 0.2 µm thick Pt film and a 0.2 µm thick Au film .

The first adhesion layer 103a is formed on the Z-axis negative side surface of the first electrode 102a, and the second adhesion layer 103b is formed on the Z-axis positive side surface of the second electrode 102b. The first adhesion layer 103a and the second adhesion layer 103b are each a eutectic solder made of a gold-tin alloy containing Au and Sn in proportions of 70% and 30%, respectively.

The semiconductor laser element 1 is mounted on the sub-assembly part 100 such that the p side (the electrode member 50 side) of the semiconductor laser element 1 is connected to the sub-assembly part 100. In the 10 The assembly form shown is therefore an assembly with a downward connection (junction-down), whereby the contact electrode 52 of the semiconductor laser element 1 is connected to the first adhesion layer 103a of the subassembly part 100.

A wire 110 is connected to each of the n-side electrode 80 of the semiconductor laser element 1 and the first electrode 102a of the subassembly part 100 by wire bonding. Accordingly, a voltage can be applied to the semiconductor laser element 1 via the wires 110.

In the 10 The semiconductor laser device 2 shown is mounted with a junction-down such that the p-side (the electrode member 50 side) of the semiconductor laser element 1 is connected to the sub-mounting part 100. However, an assembly with an upward connection (junction-up) can also be used, in which the n-side electrode 80 of the semiconductor laser element 1 is connected to the subassembly part 100. Furthermore, for the semiconductor laser device 2, a form of assembly in which separate sub-assembly parts are respectively connected to the electrode member 50 and the n-side electrode 80 can be used.

The following is with reference to 11 until 12(b) the shape of the side surface 40b of the ridge part 40a is described.

11 is a schematic view showing sizes of the side surface 40b of the ridge portion 40a. Similar to 1 , is 11 a plan view schematically showing a configuration of the semiconductor laser element 1.

The width in the x-axis direction of the ridge part 40a (hereinafter simply referred to as “width”) changes continuously and cyclically in correspondence to the position in the Y-axis direction (wave guiding direction), with a part having a large width and a part having a small width are arranged alternately in the Y-axis direction.

Here, the local maximum value of the width of the ridge part 40a is defined as Wa, and the local minimum value of the width of the ridge part 40a is defined as Wb. The distance in the Y-axis direction from the position where the width of the ridge part 40a has the local maximum value Wa to the position adjacent thereto on the positive side of the Y-axis, within the positions where the width of the ridge part 40a has the local has minimum value Wb is defined as La. The distance in the Y-axis direction from the position where the width of the burr part 40a has the local maximum value Wa to the position adjacent thereto on the negative side of the Y-axis within the positions where the width of the burr part 40a has the local minimum value Wb is defined as Lb. The side surface 40b, which extends from the position where the width of the ridge part 40a has the local maximum value Wa to the position where the width of the ridge part 40a has the local minimum value Wb, has a linear shape in a plan view . The angle between the Y-axis direction and the side surface 40b extending from the position at which the width of the ridge part 40a has the local maximum value Wa to the positive side of the Y-axis is defined as θa. The angle between the Y-axis direction and the side surface 40b extending from the position where the width of the ridge part 40a has the local maximum value Wa to the negative side of the Y-axis is defined as θb.

$$\mathrm{\theta }\text{b}=\text{arctan}\left\{\left(\text{Wa}-\text{Wb}\right)/\left(2\times \text{Lb}\right)\right\}$$

The relationship between θa, θb, Wa, Wb, La and Lb is represented by the following formulas (1), (2). $$\mathrm{\theta }\text{a}=\text{arctan}\left\{\left(\text{Wha}-\text{Wb}\right)/\left(2\times \text{La}\right)\right\}$$

$$\mathrm{\theta }\text{b}=\text{arctan}\left\{\left(\text{Wha}-\text{Wb}\right)/\left(2\times \text{Lb}\right)\right\}$$

In this embodiment, the angles θa, θb are each set larger than a critical angle θc. The critical angle θc is the maximum value of the angle at which the laser light is completely reflected on the side surface 40b of the ridge part 40a. That is, the angle θa, θb is set to satisfy formula (3). $$\mathrm{\theta }\text{a}>\mathrm{\theta }\text{c and}\mathrm{\theta }\text{b}>\mathrm{\theta }\text{c}$$

If the angle θa, θb is set larger than the critical angle θc, light in the higher order mode can be reduced and the proportion of light in the fundamental mode can be increased, which will be discussed below with reference to 13(a) is described.

A setting example of Wa, Wb, La, Lb, θa and θb is described below.

For example, the width of the ridge part 40a is not smaller than 1 µm and not larger than 100 µm. To prompt. that the semiconductor laser element 1 is operated with a high light output (e.g. Watt class), the local maximum value Wa of the width of the ridge part 40a must be set not smaller than 10 μm and not larger than 50 μm. The smaller the local minimum value Wb of the width of the ridge part 40a, the more the higher order mode component can be reduced. However, if the local minimum value Wb is too small, the fundamental mode component (transverse fundamental mode component) is also reduced. On the other hand, if the local minimum value Wb of the width of the ridge part 40a is made large, the reduction effect for the higher order mode component is reduced. In order to efficiently suppress the higher order mode component while maintaining the intensity according to the fundamental mode, the local minimum value Wb of the width of the ridge part 40a can be set to not less than 1/4 and not greater than 3/4 of the local maximum value Wa of the width be set.

When the distance La, Lb is decreased, the angle θa, θb is increased, so that formula (3) is easily satisfied. On the other hand, if the distance La, Lb is reduced too much, the number of Parts where the width of the ridge part 40a is small are reduced in the range of the length in the Y-axis direction of the semiconductor laser element 1. This reduces the suppression effect for the higher order mode. In this embodiment, Wa=16 µm, Wb=10 µm and La=Lb=30 µm are set. This results in θa=θb=5.7°.

As long as the conditions of formulas (1), (2) are met, La≠Lb can be allowed. In the case of La≠Lb, although light passes back and forth in the Y-axis direction in the resonator, the higher-order mode loss can be provided differently between the forward path and the reverse path. For example, in the case of La>Lb, the loss on the higher order mode can be reduced when light propagates from the end face 1b to the end face 1a.

As described above, the groove part 70 is arranged on the outside of the side surface 40b of the ridge part 40a. Here, when the ridge part 40a and the groove part 70 are separated from each other by a certain distance Dd in the width direction (the X-axis direction) of the ridge part 40a, the formula (4) must be satisfied in order for the groove part 70 to have an effect on the propagation of light on the outside of the ridge part 40a. $$\text{Wb}+2\times \text{Dd}<\text{Wha}$$

At this time, if the distance Dd is too small, the proportion under the influence of the groove part 70 in the fundamental mode component increases, thereby increasing the loss of the fundamental mode. Therefore the distance Dd must have a certain size. From studies carried out by the inventors, it was found that when the distance Dd is not smaller than 1 µm, the loss in the fundamental mode component can be suppressed. In the X-axis direction, the end of the groove part 70 may be on the side opposite to the ridge part 40a at the same position as the side surface 40b of the ridge part 40a where the width has the local maximum value Wa, or further outward. In this embodiment, Dd=2 µm, and in the Wa has.

The following describes how the critical angle θc is obtained.

Here, using an equivalent refractive index method, a three-dimensional structure of the ridge portion 40a is provided by a waveguide structure with a two-dimensional plate. At the center position in the Accordingly, at the center position in the X-axis direction of the groove part 70, an equivalent refractive index no at that position is calculated using the thickness and refractive index of each layer. The equivalent refractive index ni is the effective refractive index on the inside of the ridge part 40a, and the equivalent refractive index no is the effective refractive index on the outside of the ridge part 40a. In this embodiment, ni>no is always fulfilled by the formation of the ridge part 40a.

Then, using Schnellius' law, the maximum value of the angle when an overall reflection condition is satisfied, that is, the critical angle θc, is calculated. The critical angle θc is calculated by the formula (5). $$\mathrm{\theta }\text{c}=90°-\text{arcsin}\left(\text{no/no}\right)$$

For example, if ni=2.535 and no=2.527, θc=4.6° is calculated based on formula (5). Using the thus calculated θc, Wa, Wb, La and Lb are set so that the formulas (1) to (3) are satisfied.

An example of the procedure for actually determining each set value is described below.

12(a) is a graph showing the relationship between a refractive index difference (ni-no) between the inside and outside of the ridge part 40a and the critical angle θc. In 12(a) the horizontal axis represents the refractive index difference (ni-no) and the vertical axis represents the critical angle θc. The curve diagram in 12(a) was created based on formula (5).

As described above, when the equivalent refractive index ni, no is calculated using the thickness and refractive index of each layer, the critical angle θc can be based on the formula (5) or the curve diagram of 12(a) be calculated.

12(b) is a curve diagram showing the relationship between the distance La and the local minimum value Wb, which satisfies the formula (3) when the local maximum value Wa is fixed at 16 µm and the critical angle θc is 2.6°, 3, 6°, 4.6°, 5.6° or 6.6°. In 12(b) the horizontal axis represents the distance La and the vertical axis represents the local minimum value Wb.

In an area under each straight line in 12(b) the condition of formula (3) is fulfilled. Therefore, when the local minimum value Wb and the distance La are set to be included in the area below the straight line corresponding to the critical angle θc, the angle θa can be set larger than the critical angle θc. And also with respect to the distance Lb, when the local minimum value Wb and the distance Lb are set to be included in the area below the straight line corresponding to the critical angle θc, the angle θb can be larger than the critical angle θc be set.

In this way, the critical angle θc is calculated based on the equivalent refractive indices ni and no on the inside and outside of the ridge part 40a, and the local maximum value Wa, the local minimum value Wb and the distance La, Lb can be set based on the calculated θc become. Accordingly, formula (3) is satisfied, so that light can be reduced in the higher order mode.

The following is with reference to an in 13(a) and 13(c) shown comparative example 1 and one in 14 Comparative Example 2 shown describes the advantages and disadvantages of Comparative Examples 1 and 2.

13(a) Fig. 10 is a plan view schematically showing a configuration of a semiconductor laser element according to Comparative Example 1. In a lower part of 13(a) Curve diagrams showing examples of the light distribution in the fundamental mode and the higher order mode in the X-axis direction are provided.

In Comparative Example 1, no groove part 70 is provided compared to the embodiment described above. In the semiconductor laser element of Comparative Example 1, during laser oscillation, light propagates in the Y-axis direction in the ridge portion 40a. At this time, the overall reflection condition on the inside and outside of the ridge part 40a is not satisfied (because the formula (3) is satisfied, so the light generally propagates in the Y-axis direction even if a part where the width of the ridge part 40a is small, is present. In 13(a) arrows drawn in dashed lines indicate how the light progresses. In a part where the width of the ridge part 40a is small, the light propagates slightly on the inside under the influence of the refractive index difference between the inside and the outside of the ridge part 40a. However, because the overall reflection condition is not satisfied, most of the light propagates in the Y-axis direction while passing through the outside of the ridge portion 40a.

Here, the light propagating on the ridge part 40a includes a light in the fundamental mode and a light in the higher order mode as in the curve diagrams in the lower part of 13(a) shown. As shown in Comparative Example 1, when the formula (3) is satisfied, the light component of the higher order mode is lost due to the side surface 40b of the ridge portion 40a and the proportion of the fundamental mode can be increased.

13(b) and 13(c) are cross-sectional views each schematically showing configurations of the semiconductor laser of Comparative Example 1 of 13(a) for an A11-A12 cross-section and an A21-A22 cross-section seen from the positive Y-axis direction. In 13(b) and 13(c) For the sake of simplicity, only the substrate 10, the first semiconductor layer 20, the active layer 32 and the second semiconductor layer 40 are shown.

As in 13(b) As shown, the semiconductor laser element is configured such that at a position where the width of the ridge portion 40a is large, the light propagating in the ridge portion 40a is limited to the vicinity of the active layer 32 as indicated by the light distribution DL1 in the fundamental mode. In this case, light traveling in the ridge portion 40a is less likely to overlap the substrate 10.

However, as in 13(c) shown, at a position where the width of the ridge portion 40a is small, light propagating on the outside of the ridge portion 40a as indicated by the light distribution DL2 in the fundamental mode is pressed downward toward the side of the substrate 10 because of the thickness of the p-side cover layer 42 is small on the outside of the ridge part 40a. Therefore, excitation in a higher order mode in the vertical direction, referred to as a substrate mode, is caused between the active layer 32 and the first semiconductor layer 20 and between the first semiconductor layer 20 and the substrate 10. When this substrate mode is caused, a ripple is caused in the vertical far field pattern. Such a ripple increases particularly due to a higher order mode having a peak in light intensity on the outside of the ridge portion 40a.

14 is a plan view schematically showing a configuration of a semiconductor laser element according to Comparative Example 2. In 14 Curve diagrams schematically showing examples of light distribution in the fundamental mode and the higher order mode in the X-axis direction are provided.

In Comparative Example 2, compared to the embodiment described above, there is no Groove part 70 is provided and instead of the burr part 40a, a burr part 200 is formed in an upper part of the second semiconductor layer 40. In Comparative Example 2, the overall reflection condition on the inside and outside of the ridge part 200 is satisfied. In Comparative Example 2, instead of formula (3), the relationships θa<θc and θb<θc are satisfied.

In Comparative Example 2, because formula (3) is not satisfied, light in the higher order mode cannot be reduced in the manner as in Comparative Example 1. However, in Comparative Example 2, ripple in the vertical far-field pattern caused in the case of Comparative Example 1 can be suppressed.

In the semiconductor laser element of Comparative Example 2, the refractive index difference between the inside and the outside of the ridge part 200 satisfies the overall reflection condition. As indicated by the arrows drawn in dashed lines in 14 stated, light in the ridge portion 200 is reflected on one side surface 201 of the ridge portion 200, and the reflected light passes through the other side surface 201 of the ridge portion 200 to be irradiated onto the outside of the ridge portion 200. That is, the light emitted as laser light to outside the semiconductor laser element does not propagate on the outside of the ridge portion 200. The substrate mode caused in Comparative Example 1 is suppressed in the structure of the burr part 200 of Comparative Example 2. Therefore, with the semiconductor laser element of Comparative Example 2, ripple in the vertical far field pattern can be suppressed.

15 contains curve diagrams showing a result of an experiment on a vertical far-field pattern obtained when the structures of the ridge parts of the semiconductor laser elements according to Comparative Examples 1 and 2 are changed.

Regarding 11 , which shows the sizes of components, in this experiment La=Lb and Wa=16 µm were set fixed and the distance La was changed in a range from 15 µm to 90 µm with an interval of 15 µm. The local minimum value Wb of the width was changed in a range of 4 µm to 10 µm with an interval of 2 µm. In this experiment, similar to Comparative Examples 1 and 2, no groove part 70 was provided.

15 shows the vertical far field pattern at a light output of 1 W in the semiconductor laser elements with these corresponding structures. In every curve diagram of 15 the vertical axis represents the light intensity normalized to the maximum value and the horizontal axis represents the normalized angle. In 15 Curves of the vertical far-field pattern based on the semiconductor laser element of Comparative Example 1, which satisfy the relationship of formula (3), and curves of the vertical far-field pattern based on the semiconductor laser element of Comparative Example 2, which do not satisfy the relationship of formula (3), are represented by a dashed line separated from each other.

As shown in the curves on the left side of the dashed line, in the semiconductor laser element (Comparative Example 1) satisfying θa>θc and θb>θc, a ripple (disturbance) is caused in the vertical far-field pattern. On the other hand, as shown in the curves on the right side of the dashed line, in the semiconductor laser element (Comparative Example 2) satisfying θa<θc and θb<θc, no ripple is caused in the vertical far field pattern. And the smaller the local minimum value Wb of the width, the greater the intensity of the ripple becomes. Namely, the smaller the local minimum value Wb of the width, the larger the proportion of light passing through the outside of the ridge part. In the curves on the left side of the dashed line, the waviness becomes smaller in a structure that is closer to the structure satisfying the relationship θa<θc and θb<θc. The reason for this is that the proportion of light satisfying the condition θa<θc and θb<θc, i.e. the overall reflection condition, is larger.

As described above, in the semiconductor laser element of Comparative Example 1, which satisfies the relationship of formula (3), ripple is caused in the vertical far-field pattern. On the other hand, in the semiconductor laser element of Comparative Example 2, which does not satisfy the relationship of formula (3), the probability of causing ripple in the vertical far field pattern is smaller, but it is difficult for light in the higher order mode as with reference to 14 to reduce described. In contrast, the semiconductor laser element 1 according to this embodiment satisfies the relationship of formula (3) and includes the groove part 70 for suppressing ripple in the vertical far field pattern.

Regarding 16(a) to 16(c) Effects of the groove part 70 of the semiconductor laser element 1 according to the present embodiment will be described.

16(a) is a plan view schematically showing a configuration of the semiconductor laser element 1 according to the embodiment. In a lower part of 16(a) Curve diagrams showing examples of light distribution in the fundamental mode and the higher order mode in the X-axis direction are included.

In the embodiment, similar to Comparative Example 1 described above, light generally propagates in the Y-axis direction as indicated by the dashed arrows. Here, the light propagating from the ridge portion 40a includes a fundamental mode light and a higher order mode light as shown in the curve diagrams in the lower part of FIG 16(a) shown. In the embodiment, formula (3) is satisfied as in Comparative Example 1. The light component in the higher order mode is lost due to the side surface 40b of the ridge portion 40a, and the proportion of the fundamental mode can be increased.

16(b) and 16(c) are cross-sectional views each schematically showing configurations of the semiconductor laser element 1 of the embodiment of FIG 16(a) for an A31-A32 cross-section and an A41-A42 cross-section seen from the positive Y-axis direction. In 16(b) and 16(c) For the sake of simplicity, only the substrate 10, the first semiconductor layer 20, the active layer 32, the second semiconductor layer 40 and the groove part 70 are shown.

As in 16(b) As shown, at a position where the width of the ridge portion 40a is large, similarly to Comparative Example 1, light propagating in the ridge portion 40a is less likely to overlap the substrate 10 as indicated by the light distribution DL3 in the fundamental mode.

As in 16(c) As shown, at a position where the width of the ridge portion 40a is small, the groove portion 70 is formed on the outside of the ridge portion 40a, and the light passing through the outside of the ridge portion 40a passes directly above the groove portion 70.

The groove part 70 is filled with air as described above and therefore has a refractive index that is smaller than that of the first semiconductor layer 20. Therefore, when the groove part 70 having a small refractive index is formed at the bottom (on the first semiconductor layer 20 side with respect to the active layer 32) in a light transmission region, downward movement of the light is restricted. So, a downward movement of the light that has advanced to the outside of the ridge part 40a and arrived directly above the groove part 70 is suppressed. That's why it's like in 16(c) 1 shows a light distribution DL4 in the fundamental mode of laser light according to this embodiment at an upper position relative to the light distribution DL2 in the fundamental mode of laser light when the groove part 70 is not provided (Comparative Example 1). Accordingly, movement of the light to the substrate 10 can be reduced, thereby reducing the substrate mode. Thereby, with the semiconductor laser element 1 of this embodiment, ripple in the vertical far field pattern is suppressed.

<Effects of Embodiment>

According to the embodiment, the following effects are achieved.

Because the angle θa, θb between the side surface 40b of the ridge part 40a and the waveguide direction (the Y-axis direction) is set larger than the critical angle θc, the laser light in the higher order mode is cut off and the proportion of the laser light in the fundamental mode is increased . The groove part 70 is formed at least on the substrate 10 and the first semiconductor layer 20, and is disposed on the outside of the side surface 40b at least where the width of the ridge part 40a is small. Accordingly, as with reference to 16(c) described a downward movement of the distribution position of the laser light propagating on the ridge part 40a (of the waveguide WG) is less likely, thereby suppressing ripple in the vertical far field pattern. Thus, while ripple in the vertical FPP is suppressed, the proportion of the fundamental mode can be increased.

The groove part 70 is formed in the substrate 10 and in the first semiconductor layer 20. Therefore, while the distribution position of the laser light propagating on the ridge part 40a (the waveguide WG) is maintained at the light emitting layer 30, downward movement of the distribution position of the laser light can be effectively suppressed.

In a plan view, the groove part 70 is arranged along the side surface 40b on the outside of the side surface 40b of the ridge part 40a. In particular, the groove part 70 is arranged parallel so that it passes through with a distance Dd (see 11 ) is spaced apart in the width direction with respect to the side surface 40b. With the minimal arrangement of the groove part 70, downward movement of the distribution position of the laser light propagating on the ridge part 40a (the waveguide WG) can be effectively suppressed.

The composition ratio (Ga/N) of Ga to N on the surface of the groove part 70 in the first semiconductor layer 20 is higher than the composition ratio (Ga/N) of Ga to N inside the first semiconductor layer 20. If the Ga ratio of the groove part 70 is enlarged in this way, the light absorption effect is increased. Accordingly, unnecessary laser light can be used in the higher order mode in the night bility of the groove part 70 can be absorbed, whereby the higher order mode component can be reduced.

Because as in 2 As shown, the cross section of the groove part 70 has a rectangular shape, the inner end and the outer end in the X-axis direction of the groove part 70 become parallel to the Z-axis direction. Accordingly, a cut surface is caused at each layer in the vicinity of the position P1 at the inner end and in the vicinity of the position P2 at the outer end. When a cut surface is caused at each layer at the position P1, P2, the laser light can be scattered in the higher order mode, which can reduce the higher order mode component.

The angle θa, θb between the side surface 40b of the ridge part 40a and the wave guide direction (the Y-axis direction) is set larger than the critical angle θc. In this case, the critical angle θc is the maximum value of the angle at which the laser light is completely reflected on the side surface 40b. Then, with the side surface 40b of the ridge part 40a, the higher order mode component propagating on the ridge part 40a can be reduced and the proportion of the fundamental mode can be increased.

<Modifications>

An embodiment of the present invention has been described above, but the present invention is not limited to the embodiment described herein, which can also be modified in various ways.

For example, in the embodiment described above, the interior of the groove part 70 is made of air. However, the invention is not limited to this, and a dielectric layer implemented by a silicon oxide film (SiO ₂ ) may also be included as a lower refractive index part having a refractive index smaller than that of the first semiconductor layer 20 Groove part 70 may be formed. Alternatively, a gap may be provided between a dielectric layer and the first semiconductor layer 20. For example, in the groove part 70, a dielectric 71 may be disposed as shown in the following modifications 1 to 3.

In modification 1 of 17(a) , the modification 2 of 17(b) and modification 3 of 18 In contrast to the above embodiment, the dielectric 71 is arranged on the bottom 70a of the groove part 70. The refractive index of the dielectric 71 is smaller than the refractive index of the first semiconductor layer 20 and larger than the refractive index of air. The dielectric 71 is implemented by, for example, a silicon oxide film (SiO ₂ ).

In Modifications 1 and 2, a gap 72 is disposed between the first semiconductor layer 20 and the dielectric 71, with the lower surface (the surface on the negative side of the Z axis) of the dielectric 71 at an upper position relative to the upper surface of the substrate 10 is located. In modification 1, the gap 72 is arranged between the left and right ends of the dielectric 71 and the side surface of the groove part 70. In modification 2, the dielectric 71 covers the bottom 70a, and the gap 72 is disposed at the boundary (corner part) between the bottom 70a and the side surface of the groove part 70. In modification 3, the lower surface (the surface on the negative side of the Z axis) of the dielectric 71 is disposed between the upper surface and the lower surface of the substrate 10.

When the dielectric 71 is to be formed in the groove part, the dielectric 71 is formed on the entire surface on the negative side of the Z-axis of the substrate 10 in the in 8(b) shown condition. Then, when the third protective film 93 is removed using a solvent that can only remove the third protective film 93, the dielectric 71 on the third protective film 93 is removed by lift-off, so that the dielectric 71 can be formed only in the groove part 70.

When the dielectric 71 is disposed in the groove part 70 as in modifications 1 to 3, the refractive index in the vicinity of the groove part 70 changes smoothly, so that scattering of light in the fundamental mode due to a significant change in the refractive index can be suppressed. Accordingly, the fundamental mode ratio can be relatively increased. When the gap 72 is arranged as in modifications 1 and 2, a mechanical stress caused by a difference in thermal expansion coefficient between the first semiconductor layer 20 and the dielectric 71 can be relaxed. Therefore, stable laser operation can be realized even at high temperatures. In the modification 2, the entry of foreign matter from outside into the corner part of the groove part 70 serving as a passage for the laser light can be prevented, whereby variation in the semiconductor laser element 1 can be suppressed. And in the modification 3, because the dielectric 71 is embedded up to the substrate 10, the strength of the semiconductor laser element 1 can be increased. Accordingly, breakage of the semiconductor laser element 1 due to a load at the time of Assembly can be suppressed. As a result, the reliability of the semiconductor laser element 1 can be increased.

In modifications 1 to 3, the dielectric 71 is implemented by a silicon oxide film (SiO ₂ ), but the invention is not limited thereto and another material having a refractive index smaller than that of the first semiconductor layer 20 may also be used. Also in this case, similarly to modifications 1 to 3, the refractive index in the vicinity of the groove part 70 can be greatly changed by the dielectric 71, and the occurrence of ripple in the vertical FPP can be suppressed by the groove part 70. Examples of the material of the dielectric 71 are SiN (refractive index: 2.07), Al ₂ O ₃ (refractive index: 1.79), AlN (refractive index: 2.19) and ITO (refractive index: 2.12). When the dielectric 71 is formed of ITO, light in the higher order mode can be suppressed more.

The dielectric 71 may be formed of a material (for example, carbon or amorphous silicon) that absorbs light from the light-emitting layer 30. When the dielectric 71 is formed of a material that absorbs light from the light emitting layer 30, the laser light in the higher order mode is cut off, whereby the proportion of the laser light in the fundamental mode can be increased.

In the embodiment described above, as in 1 shown, the groove part 70 is arranged on the outside of the side surface 40b where the width of the ridge part 40a has the local minimum value and is not arranged on the outside of the side surface 40b where the width of the ridge part 40a has the local maximum value. However, the invention is not limited to this, and the groove part 70 may be as in modification 4 of 19 shown can also be arranged over the entire outside of the side surface 40b of the ridge part 40a.

In modification 4 of 19 the groove part 70 is arranged at a certain distance from the side surface 40b on the outside of the side surface 40b. The inner end of the groove part 70 is parallel to the side surface 40b so that it corresponds to a cyclic change in the width direction of the side surface 40b. The outer end of the groove part 70 is parallel to the Y-axis direction. In this case, because the n-side electrode 80 disposed in the vicinity of the waveguide WG at the center and the n-side electrodes 80 disposed on the left and right sides of the waveguide WG are on the surface on the negative side of the Z-axis of the substrate 10 are separated from each other, the wire 110 (see 10 ) set such that the three n-side electrodes 80 are conductive to one another. Alternatively, the three n-side electrodes 80 may be conductive to each other by also forming an n-side electrode in the groove portion 70. In modification 4 of 19 The outer end of the groove part 70 may also be parallel to the side surface 40b to correspond to a cyclic change in the width direction of the side surface 40b.

In the embodiment described above, as in 1 Shown in a plan view, the side surface 40b is inclined in a direction at the angle θa, θb with respect to the Y-axis direction, but is not in an oblique direction as shown in FIG 1 shown must extend. For example, as in modification 5 of 20 shown, the side surface 40b consists of a part that is parallel to the Y-axis direction and a part that is parallel to the X-axis direction.

In modification 5 of 20 The part of the side surface 40b where the width of the ridge part 40a has the local minimum value and the part of the side surface 40b where the width of the ridge part 40a has the local maximum value extend in the Y-axis direction, respectively, and are the part the side surface 40b where the width has the local minimum value and the part of the side surface 40b where the width has the local maximum value are connected to each other by a part of the side surface 40b that is parallel to the X-axis direction. Also in this case, the width of the ridge part 40a changes cyclically in accordance with the position in the waveguide direction (the Y-axis direction) of the ridge part 40a. The angle between the side surface 40b of the ridge part 40a and the wave guiding direction (the Y-axis direction), that is, the angle between the part of the side surface 40b that is parallel to the X-axis direction and the wave guiding direction (the Y-axis direction) is larger as the critical angle θc. The groove part 70 has a rectangular shape in a plan view and is disposed on the outside of the part of the side surface 40b where the width of the ridge part 40a has the local minimum value. Therefore, in modification 5, a ripple in the vertical far field pattern is also suppressed and the proportion of the fundamental mode can be increased.

In the embodiment described above, the side surface 40b of the ridge portion 40a has a linear shape in a plan view. However, as long as the condition of formula (3) is satisfied, the side surface 40b can have a curved shape in a plan view.

In the embodiment described above, the cross section of the groove part 70 is right angular shape, although the invention is not limited to this and the cross section can also have a trapezoidal shape, a triangular shape, an elliptical shape, etc.

In the embodiment described above, the groove part 70 is formed in the substrate 10 and in the first semiconductor layer 20, but the invention is not limited thereto and the groove part 70 also extends over the n-side light guide layer 31, the first semiconductor layer 20 and the substrate 10 can extend. The groove part 70 may be formed from the lower surface of the substrate 10 to the n-side light guide layer 31 and connected to the substrate 10, the first semiconductor layer 20 and the n-side light guide layer 31.

In the embodiment described above, the semiconductor laser element 1 and the semiconductor laser device 2 do not necessarily have to be used in processing a product and may also be used for another purpose.

In addition, various further modifications may be made to the described embodiment without departing from the scope of the invention as defined by the claims.

LIST OF REFERENCE SYMBOLS

1

semiconductor laser element

10

Substrate

20

first semiconductor layer

30

light emission layer

32

active layer

40

second semiconductor layer

40a

burr part

40b

side surface

70

groove part

71

dielectric

72

space

Claims (8)

Semiconductor laser element comprising: a substrate, a first semiconductor layer arranged above the substrate, a light emission layer arranged over the first semiconductor layer, a second semiconductor layer disposed over the light emitting layer, and a groove part formed at least on the substrate and the first semiconductor layer, wherein the second semiconductor layer has a ridge part for guiding the laser light generated in the light emission layer, wherein the width of the ridge part changes cyclically in accordance with the position in a waveguiding direction of the ridge part, wherein the angle between a side surface of the ridge part and the wave guiding direction is larger than a critical angle defined by an effective refractive index on an inside of the ridge part and an outside of the ridge part, respectively, and wherein the groove part is arranged on the outside of the side surface at least where the width of the ridge part is small. Semiconductor laser element Claim 1 , where: the composition ratio of Ga to N at a surface of the groove part in the first semiconductor layer is larger than the composition ratio of Ga to N inside the first semiconductor layer. Semiconductor laser element Claim 1 or 2 , wherein: a dielectric with a refractive index smaller than that of the first semiconductor layer is arranged in the groove part. Semiconductor laser element Claim 3 , wherein: a gap is arranged between the first semiconductor layer and the dielectric. Semiconductor laser element Claim 3 or 4 , where: the dielectric is a material that absorbs light from the light-emitting layer. Semiconductor laser element Claim 5 , where: the dielectric is made of carbon. Semiconductor laser element Claim 3 or 4 , where: the dielectric is implemented by a silicon oxide film. Semiconductor laser element according to one of the Claims 1 until 7 , where: the critical angle is a maximum value of an angle at which the laser light is completely reflected on the side surface.

Images